The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An internal combustion engine burns a mixture in which fuel and air are mixed in a predetermined ratio using a predetermined ignition method to generate power using explosion pressure. Generally, a camshaft is driven by a timing belt connected to a crankshaft which converts linear motion of a cylinder due to the explosion pressure into rotational motion to actuate an intake valve and an exhaust valve. While the intake valve is open, air is drawn into a combustion chamber, and while the exhaust valve is open, gas that has been combusted in the combustion chamber is exhausted.
The opening/closing timing and opening duration of the intake valve and the exhaust valve should be adjusted depending on operating conditions of the engine such as rotation speed or load so that optimal engine performance can be ensured. With this in mind, a continuous variable valve duration (CVVD) apparatus that adjusts the opening duration of the intake valve and the exhaust valve has been developed.
Recently, an engine having a CVVD apparatus has been applied to various hybrid vehicles such as hybrid electric vehicles (HEV) or plug-in hybrid electric vehicles (PHEV).
A hybrid vehicle may run in any one of the following driving modes: EV mode in which the hybrid vehicle is only driven by power of a motor generator; HEV mode in which the hybrid vehicle is driven by power of the engine and power of the motor generator; and engine driving mode in which the hybrid vehicle is only driven by power of the engine. In operating conditions in which the engine is required to be driven (HEV mode or engine driving mode), a CVVD value corresponding to a torque required by a driver may be determined and the CVVD apparatus may be driven according to the determined CVVD value to start the engine.
However, while the engine is being started depending on the CVVD value corresponding to the torque required by the driver, the engine starting RPM may become relatively high, which may make it difficult to synchronize RPM of the engine with RPM of an automatic transmission and/or RPM of the motor generator.
The above information described in this background section is provided to assist in understanding the background of the inventive concept, and may include any technical concept which is not considered as the prior art that is already known to those skilled in the art.